Electronic camera with dual exposure and selective recording

ABSTRACT

An electronic camera having an image sensor responsive to a preliminary exposure for producing an output signal, a computing circuit for computing a proper exposure condition on the basis of the signal, and a compensating circuit for compensating the exposure value in accordance with the proper exposure condition is provided with a compensation prohibiting circuit for prohibiting the exposure compensation by the preliminary exposure by taking into account the object condition and the exposure mode.

This is a continuation application under 37 CFR 1.62 of priorapplication Ser. No. 07/970,288, filed Nov. 2, 1992, (aban.) which is adivisional of Ser. No. 07/325,547, filed Mar. 20, 1989 (now issued asU.S. Pat. No. 5,189,519).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electronic camera capable of setting anexposure value with or without selection of an exposure compensation bythe preliminary exposure.

2. Description of the Related Art

The electronic camera using the image sensor such as CCD in recordingpictures on the magnetic disc or the like has a narrower latitude to thequantity of light than the ordinary photographic camera using asilver-halide film and is, therefore, required to make exposures with ahigher accuracy. In this respect, there have been many previousproposals. As disclosed in, for example, U.S. Pat. Nos. 4,523,101 and4,734,777, prior to the main exposure, a preliminary exposure is made onthe image sensor. Based on the level of the output signal for this timeof the image sensor, the exposure value is compensated in controllingthe main exposure. Also, the photographer of good experience sometimesfavors the manual exposure mode where a proper exposure value can beobtained by manually controlling the exposure parameter setting means.

In the conventional electronic camera, however, the use of thecapability of making the preliminary exposure always leads to occurrenceof the compensation of the exposure value by the level of thepreliminary output of the image sensor. Therefore, even when thephotographer sets a desired exposure value by his hand as he considersit more suitable than the computed one, re-compensation by thepreliminary exposure would take place, thus giving rise to a problemthat the desired exposure control cannot be made.

Another problem of the above-described conventional example is thatsince every time a shot is to be taken, the preliminary exposure must becarried out and, after that, the main exposure occurs, the time gap fromthe moment at which the release button has been pushed down to themoment at which the actual picture is taken is very long. This isdisadvantageous when achieving introduction of a capability of taking aseries of continuous shots at a high frame rate into the camera.

Again, the image sensor has, despite large consumption of electricalenergy, to be driven twice for every one picture, as has been describedabove. Therefore, the battery to be used must be of large capacity. Thishas been an obstacle for minimization of the size of the camera body.

The conventional camera in any photographic situation performs twice theopening-and-closing operation. In the case of a long exposure time,therefore, the successive two shutter sounds are heard discretely ofeach other, irritating the ear. In addition to this problem, there isanother one in which the diaphragm has to be maintained stationary inthe adjusted position for a long time.

SUMMARY OF THE INVENTION

With such problems in mind, the invention has been made, and its objectis to provide an electronic camera in which when an exposure value hasbeen set manually, the re-compensation by the preliminary exposure isprohibited from occurring, thus making it possible to always makedesired exposure controls.

Another object of the invention is in view of the foregoing to providean exposure control device which enables the frame rate of shootings tobe increased and the size of the electronic camera body to be minimized.

Also, the invention is to eliminate the problems inherent in thehalf-open type shutter.

Another object of the invention is to provide an exposure apparatuswhich can control exposure always with high accuracy regardless ofwhether or not the running characteristic of the opening and closingmembers for opening and closing an aperture opening for exposure, orother characteristics, vary and in which when a photographic situationwhere there is no need to carry out the two cycles of opening andclosing operation of the opening and closing members for one picture isencountered, only one cycle can be made sufficient.

In an embodiment of the invention, an electronic camera having computingmeans for computing a proper exposure condition on the basis of thepreliminary exposure on the image sensor in the form of a signal outputfrom the image sensor and compensating means for compensating theexposure by the computed condition is provided with compensationprohibiting means responsive to manual setting of an exposure value forprohibiting the exposure compensation by the preliminary exposure.

In another embodiment of the invention, the electronic camera having theaforesaid computing means and the compensating means is provided withcompensation prohibiting means responsive to setting of a flash exposuremode for prohibiting the exposure compensation by the preliminaryexposure.

Since, in the electronic camera of the first named embodiment, thepreliminary exposure is prohibited from compensating the exposure whenthe exposure value has been set manually, it is always possible to makethe desired exposure control.

Also, in the electronic camera of the second named embodiment, theexposure compensation by the preliminary exposure is prohibited fromoccurring when in the flash exposure mode. Thus, the desired exposurecontrol can be made too.

In yet another embodiment of the invention, an exposure control devicefor the electronic camera in which the preliminary exposure and the mainexposure controls are made is provided with control means responsive toautomatic determination of the distribution of brightness on an objectto be photographed for causing either the main exposure control alone orthe sequence of the preliminary exposure and the main exposure controlsto take place.

The invention by the embodiment described just above can perform anecessary minimum and optimum exposure control depending on thedistribution of brightness of the object.

Also, to achieve the above-described objects, in an embodiment of theinvention applied to the exposure apparatus in which the opening andclosing members such as shutter blades or diaphragm blades for openingand closing an exposure aperture are preliminarily opened and closedprior to that opening and closing operation which makes an actualexposure, then a reference value for use in the actual exposure openingand closing operation is determined on the basis of a value of thequantity of movement or the quantity of exposure detected when in thispreliminary opening and closing operation, and then when in the actualexposure opening and closing operation which is carried out after thatpreliminary opening and closing operation, the opening and closingmembers are operated according to that reference value, provision ismade of opening and closing member drive control means for selectivelyperforming that preliminary opening and closing operation depending oneither of a case where the value output from an element for measuringthe light quantity of a target to be photographed which becomes thereference value of that preliminary opening and closing operation isoutside a certain constant range and another case where it is inside therange.

Also, as necessity arises, a comparing circuit for determining the needof the preliminary opening and closing operation and a control circuitare provided, or a mode of carrying out the preliminary opening andclosing operation when the value output from the element for measuringthe light quantity of the target to be photographed is outside thecertain range, another mode of carrying it out whenever shooting, andstill another mode of not carrying it out whenever shooting is providedin combination with a switch for the photographer to select one of thesemodes.

According to this embodiment, in a case where the opening and closingoperation of the opening and closing members is determined from thevalue output from the element for measuring the light quantity of thephotographic target to take a longer time than a certain constant value,the preliminary opening and closing operation is not carried out, whileit is possible to perform the exposure opening and closing operation bymaking use of the value output from the element for measuring the lightquantity of the photographic target as the reference. Also, in theactual exposure operation, the exposure control adapted to the exposurecharacteristic or dynamic characteristic is made, and, moreover, evenwhen taking a shot which necessitates a long time of the exposureopening and closing operation, it becomes possible to take the shotwithout any sense of incompatibility. Also, depending on thephotographic condition or the intention of the photographer, even whentaking a shot of long time, a possible case where a higher accuracy ofexposure is necessary, or even when taking a shot of short time, anotherpossible case where two exposure operation is necessary are notconsidered. Therefore, the mode of carrying out the preliminary openingand closing operation in all shots, or the mode of not carrying it out,and the mode of changing over between these two cases in automaticresponse to the value from the light measuring element are provided, anda switch for selectively operating these modes by the intention of thephotographer is provided. By this provision, the apparatus becomes moreeasy to use.

Also, to achieve the above-described objects, in another embodiment ofthe invention applied to the exposure apparatus in which the opening andclosing members for opening and closing an aperture for exposure arepreliminarily opened and closed prior to an actual exposure operation,then a reference value in the actual exposure or opening and closingoperation is determined on the basis of a value such as the quantity ofmovement or the quantity of exposure detected when in this preliminaryopening and closing operation and then when in the actual exposure oropening and closing operation which is carried out after thatpreliminary opening and closing operation, the opening and closingmembers are operated according to that reference value, provision ismade of a memory circuit for storing the value obtained by thepreliminary opening and closing operation for a certain constant time,and a comparing circuit for comparing the value of the memory circuitwith a reference exposure quantity, and further provision is made of arecording deck operating in such a manner that whilst, when thedeviation difference compared with the reference value in the comparingcircuit is greater than a certain constant value, the exposure operationis carried out again based on the reference value obtained by thepreliminary opening and closing, it is when a greater difference thanthe certain constant value is not found, that the value of the memorycircuit is transferred to a recording circuit so that it is recorded.

According to this embodiment, the quantity of exposure of thepreliminary opening and closing operation is compared with the referencequantity of exposure and the data obtained from the preliminary openingand closing operation are kept in the memory circuit for the certainconstant time. In a case where the comparison value with the referencequantity of exposure does not deviate from the certain constant value,the value of the memory circuit is regarded as the actual exposurevalue, so that the second cycle of exposure or opening and closingoperation is not carried out. Also in a case where a long time isnecessary for the exposure, the second cycle of operation is abandoned.In the embodiment of the invention, therefore, in the actual exposureoperation, an exposure control adapted to the exposure characteristic ordynamic characteristic is performed. Moreover, when the exposure time islong, or when the deviation from the reference quantity of exposure isnot too large, the exposure or opening and closing operation is notcarried out for the second time. Thus, the exposure apparatus gives nosense of incompatibility and becomes able to take shots without wastage.

Other objects of the invention and its features will become apparentfrom the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a first embodiment of theinvention.

FIG. 2 is a production diagram of the entirety of the electronic camerahaving the structure of FIG. 1.

FIG. 3 is a flowchart illustrating the operation of exposure control.

FIG. 4 is a block diagram illustrating the construction of a secondembodiment of the invention.

FIG. 5 is a flowchart explaining the operation of the system of FIG. 4.

FIG. 6 is an explanation diagram illustrating the construction ofcircuitry of a third embodiment.

FIG. 7 is a perspective view illustrating a shutter mechanism of thatembodiment.

FIG. 8 is a graph explaining the running characteristic of the shuttershown in FIG. 7.

FIG. 9 is a flowchart explaining the operation of the third embodiment.

FIG. 10 is a production diagram of a fourth embodiment of the invention.

FIG. 11 is a flowchart for that embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 in block diagram shows a first embodiment of the invention. Inthe figure, 1 is a CCD as an example of an image sensor. After apreliminary exposure has been made on the CCD 1, a proper exposurecondition is computed on the basis of a signal output from the CCD 1 bya computing means 2. Responsive to the computed condition, acompensating means 3 makes a compensation on the exposure. When anexposure value has been set by hand, a compensation prohibiting means 4prohibits the aforesaid exposure compensation by the preliminaryexposure from occurring. Thus, the selection of the manual setting leadsto stop computation of the exposure by the preliminary exposure. 5 and 6are a shutter and a diaphragm for controlling the aforesaid exposure. 7is a driver for driving the shutter 5 and the diaphragm 6.

The electronic camera of the character described is enabled to selecteither of the exposure compensation by the preliminary exposure or themanual exposure setting, as has been described above. Also, though notshown in the drawings, the video signals output from the CCD 1 can berecorded on a magnetic disc in a jacket. A signal processing circuit 8for the video signals is made to include the aforesaid computing means2, while the compensating means 3 and the compensation prohibiting means4 are included in a system controller 9 which controls the entirety ofthe system.

FIG. 2 shows the entire construction of the electronic camera having theabove-described feature, further including a taking lens 10, amodulation and recording circuit 11 receptive of the video signals thatthe signal processing circuit 8 has read from the CCD 1 for producing anoutput which is recorded on the magnetic.. disc 13 by means of a head12, a sheet motor 14 for rotating the magnetic disc 13, a driver 15 fordriving the sheet motor 14, a flash unit 16 for illuminating an objectto be photographed, and an AE sensor 17 for measuring light. When aswitch 18 for light measurement is turned on, a light measurement isstarted. Another switch 19 is for initiating recording of a stillpicture. Another switch 20 is an actuator for a preliminary exposure(EXP.C). Another switch 21 is used to set the manual mode (INST. EXP.C).In the manual mode, the exposure can be finely adjusted by either ofswitches 22 and 23 (UP, DOWN). 24 is a liquid crystal display (LCD) fordisplaying the states of operation of the various portions of the systemby the liquid crystal elements.

The operation is as follows:

At first, when shooting normally (in a first mode), the photographerturns on the switch 18 to measure light by the AE sensor 17 and then theswitch 19 to initiate an exposure operation. Responsive to turning on ofthe switch 19, the system controller 9 actuates the driver 15 for thesheet motor 14 to rotate the magnetic disc 13. At the same time, basedon the signal output from the AE sensor 17, it computes an exposurecondition, i.e., an aperture value of the lens 10 and a shutter time(speed). According to this condition, the shutter 5 and the diaphragm 6are driven through the driver 7. By this, photo-signals of an objectbeing photographed are stored in the CCD 1. The CCD 1 produces the videosignals, which are then read into the signal processing circuit 8. Theprocessed video signals are recorded on the disc 13 by the modulationand recording circuit 11 through the head 12.

Next, a shooting in a second exposure mode using the preliminaryexposure, that is, with a feedback compensation, is described. Nowsuppose, for example, the upper half of the object is very bright, thenthe shutter 5 blocks the light in the corresponding area of the surfaceof the CCD 1 to the upper half of the picture. Under this condition, apreliminary exposure is made for a time previously determined (computed)on the basis of the signal output from the AE sensor 17. Then, only thatpart of the output of the CCD 1 which represents the effective imageangle (angular field) is integrated by the signal processing circuit 8.The integrated (averaged) signal is converted into a digital form in thesystem controller 9 for the purpose of checking the exposure level. Atthis time, a feedback is applied to the shutter so that the shutter timeis compensated in such a manner that the difference between the level ofthe A/D-converted signal and a reference level is reduced to zero. Thus,the camera is made ready for the main exposure followed by the actualrecording of the image.

By such an exposure compensation, the phenomenon of under-exposure bythe influence of the very bright environment such as the sky or sun inthe upper half of the picture can be prevented. Another advantage isthat for a subject of photographic principal interest, the properexposure control can be performed.

Also, in a case where the photographer desires to manually set theexposure value, he, while maintaining the switch 21 of FIG. 2 in theclosed position, pushes the switch 22 or the switch 23 down stroke bystroke. Responsive to this, the system controller 9 determines the valueof the shutter time and the aperture value as altered in such a way thatevery time the UP switch 22 is pushed down, the exposure value isshifted in steps of 1/4 EV to the over side. Also, every time the DOWNswitch 23 is pushed down, the exposure value is shifted in steps of thesame or 1/4 EV to the under side.

This exposure control provides a possibility for the user or thephotographer of experience to finely adjust the exposure based on hispersonal insight about the photographic situation. Thus, a more corrector a particular exposure aimed at a special effect can be obtained forthe individual scene.

Here, the camera is arranged to operate normally in the second mode.Therefore, responsive to the aforesaid manual setting of, for example,an exposure value of +1.5 EV step, the system controller 9 combines thelight value produced by the AE sensor 17 with the correction of +1.5 EVstep when it determines the shutter time value and the aperture value.And, since, in this case, the manual setting has been performed, thefeedback computation by the preliminary exposure is prohibited. Thus thedirect transition to the main exposure takes place. After that, thesequence in the first mode follows to record the shot picture. From thisreason, once the photographer has set the correct exposure by his ownhand, re-compensation by the preliminary exposure is not allowed to takeplace. This leads to prevent the adverse compensation from occurring.Hence, the photographer's intention can always be reflected to theexposure control.

It should be noted that the prohibition of the exposure compensation bythe preliminary exposure is not limited to the case of manual setting,but the exposure compensation is made prohibited even when in flashphotography using the flash unit 16.

FIG. 3 is a flowchart for the above-described operation.

In the following, by reference to this flowchart, the operation of thisembodiment is described in detail.

At first, whether or not the switch 19 for shot (release) is turned onis tested in a step S1. If on, then read the provisional values of theshutter time and diaphragm aperture, or Tv and Av, which have eitherautomatically been set on the basis of the light value obtained from theAE sensor 17 or by hand (step S2).

Next, whether or not the manual mode is selected by the switch 21 formanual setting is tested in a step S3. If not the manual mode, then testwhether or not the flash mode using the flash unit 16 is selected by aflash mode switch (not shown) in a step S4.

If not the flash mode in the step S4, the process then advances to astep S5 of carrying out the preliminary exposure. That is, the diaphragm6 is moved to the size of aperture opening corresponding to the Av. Withthis, a preliminary exposure (photoelectric conversion) equivalent tothe Tv is made while electronically controlling the storing time bycontrolling the time for which the light impinges on the CCD 1, or bycontrolling the interval from the clearance to the reading of the CCD 1.After that, from the concurring image signal obtained from the CCD 1 inthe step S5, the data of the brightness of the object as measured at theactual aperture is derived and the Tv is compensated in such a mannerthat the difference between it and the reference level becomes zero,being altered to Tv+ΔTv in a step S6.

Meanwhile, if the flash mode has been determined in the step S4 to beselected, then set the predetermined flash exposure value, i.e., acertain aperture value Av (for example, at the full open aperture) and avalue of shutter time Tv (for example, for the widest possible opening)in a step S7.

Also, if the manual mode has been determined in the step S3 to beselected, the process then advances straightforward to a step S8.

In the step S8, the shutter 5 and the diaphragm 6 start to be driven topositions determined based on the set values of Tv and Av in the step S2in the manual mode, or based on the preset values of Tv and Av for flashmode in the flash mode, or based on the compensated value of Tv by thepreliminary exposure and the set value of Av in the step S2 neither inthe manual mode nor the flash mode.

After that, whether or not the flash mode is selected is checked againin a step S9. If the selected mode is judged to be the flash mode, thenfire the flash unit 16 in a step S10. After the flash adjustingoperation has been done, the process advances to a step S11. Meanwhile,if it is not the flash mode, then check the passage of the Tv in thestep S11. At the termination of passage, the shutter 5 is closed in astep S12. In the next step S13, the signal output from the CCD 1 is readin synchronism with the vertical synchronizing signal of the standardtelevision signal from the driver 7, and this signal is recorded on themagnetic sheet 13 that is rotating in synchronism with the synchronizingsignal.

As has been described above, according to the embodiment of theinvention, means are provided for prohibiting the exposure compensationby the preliminary exposure when the exposure has been set manually, orwhen in flash photography, thereby giving an advantage that the reversecompensation or other erroneous compensations are avoided so that thephotographer can perform a special exposure control as desired orconsidered better by his personal experience and insight.

Next, a second embodiment of the invention is described by using FIG. 4and FIG. 5.

In the second embodiment of the invention applied to the electroniccamera having the photographic lens for forming an object image on theimage sensor, the exposure means arranged between the photographic lensand the image sensor, and a light measuring element whose area isdivided into a number of parts, provision is made of a normal-lightingand back-lighting judging circuit for determining whether the givenphotographic situation is a normal lighting condition or back lightingcondition by the output of the light measuring element, and an exposurecontrol circuit for controlling the aforesaid exposure in accordancewith the output signals of the light measuring element and the imagesensor, wherein when the normal-lighting and back-lighting judgingcircuit has determined that the situation is a normal lightingcondition, the exposure value computed by the exposure control circuiton the basis of the output signal of the light measuring element is usedin driving the aforesaid exposure means, thus directly entering the mainexposure for taking a picture without recourse to the preliminaryexposure. Also, when the normal-lighting and back-lighting judgingcircuit has determined that it is a back lighting condition, thepreliminary exposure is first carried out, then the exposure valuederived based on the output signal of the light measuring element iscompensated by using that signal output from the image sensor which isbeing produced under the condition of this preliminary exposure, andthen this compensated exposure value is used in driving the exposuremeans to carry out the main exposure for taking a picture.

This embodiment is next described in greater detail by reference to theblock diagram of FIG. 4 and the flowchart of FIG. 5.

In FIG. 4 the same reference numerals have been employed to denote thesame parts as those shown in FIGS. 1 to 3. A multi-divided lightmeasuring sensor 17' has at least two areas, one of which occupies acentral portion and the other of which lies in the marginal portion. Thecamera further includes an exposure control circuit 25, a recordingdevice 27, and a normal-lighting and back-lighting judging circuit 26for determining whether the given situation is a normal lightingcondition or back lighting condition depending on the brightnessdifference between the central portion and the marginal portion of thelight measuring sensor 17'.

In general, with the camera of such a type as described above in whichthe exposure value is determined based on the output signal of themulti-divided light measuring sensor 17', when shooting under the normallighting condition, the exposure value can be computed more or lesscorrectly. But when shooting under the back lighting condition, as themain object lies at the center of the area of the picture, the centralportion of the multi-divided light measuring sensor 17' becomes dim,while the marginal portion is bright. This causes the exposure value toshift to a faster one as it is pulled toward the higher brightness ofthe marginal portion. Therefore, the main object will be photographed asa dark patch or with no detail.

So, in this or second embodiment, as shown in FIG. 4 and FIG. 5, theprogram begins with start at a step S14. Then the multi-divided lightmeasuring sensor 17' produces an output L₁ (for the brightness of thecentral portion) and another output L₂ (for the brightness of themarginal portion) in a step S15. These outputs L₁ and L₂ are thenaveraged to obtain a value which is used for altering the aperture valueAv to Av=Av₁ and the value of shutter speed to Tv=Tv₁ on the basis of apredetermined program line (step S16). After that, whether or not L₁<<L₂ is examined in the normal-lighting and back-lighting judgingcircuit 26 for discriminating between the normal lighting condition andthe back lighting condition (step S17). If the output of this judgingcircuit 26 represents the detection of the normal lighting condition, orNO, then drive the exposure members 5 and 6 constituting the shutterand/or the diaphragm according to that value of shutter speed and/orthat aperture value which are or is determined based on the exposurevalue computed from the reliable output of the multi-divided lightmeasuring sensor 17' by the exposure control circuit 25 to obtain thecomputed exposure value, i.e., Tv=Tv₁ or Av=Av₁, thus making the mainexposure without having to make the preliminary exposure (step S20). Theelectric charge image output from the main-exposed image sensor 1 issent to the recording device 27 by the image sensor driver 7, beingrecorded on a floppy disc or the like, and the shooting is completed(step S21).

The back lighting case (when L₁ <<L₂ in the step S17) is different fromthe normal lighting case in that the preliminary exposure is carried outon the basis of the exposure value computed from the output signal ofthe multi-divided light measuring sensor 17' by the exposure controlcircuit 25, that is, at first in Tv=Tv₁, Av=Av₁ (step S18), then theelectrical signal obtained from the image sensor 1 by this preliminaryexposure is used for comparison with a predetermined reference value forthe case of optimum exposure, for example, and then the differencebetween it and the reference value is reduced to zero in order tocompensate the exposure value computed from the output signal of themulti-divided light measuring sensor 17' to Tv=Tv₂, Av=Av₂. Thus a moreproper exposure value is obtained (step S19). After that, similarly tothe normal lighting case, the exposure members 5 and 6 are driven by theshutter speed Tv=Tv₂ and/or the aperture value Av=Av₂ to make a mainexposure. Then, the electric charge image formed by this main exposureis read from the image sensor 1 and recorded.

As has been described above, by providing for the electronic camera withthe normal-lighting and back-lighting judging circuit for discriminatingbetween the normal lighting condition and the back lighting condition bythe brightness difference between the central portion and the marginalportion of the multi-divided light measuring sensor, it is possible toobtain a proper exposure in all photographic situations which may beencountered. Also, in comparison with the conventional electronic cameraof the type in which the preliminary exposure is always made by ignoringthe lighting condition and after that the main exposure is carried out,the camera of the invention, because its selecting the preliminaryexposure only in the back lighting condition, consumes far lesselectrical energy per shot, since a large quantity of electric power isrequired to drive the image sensor. Moreover, for photography under thenormal lighting condition, because the preliminary exposure is omitted,the time required for completing one cycle of shooting operation can beshortened. This enables achievement of an increase of the frame rate atwhich a series of continuous shots are taken to a higher value than washeretofore impossible.

It should be noted in connection with the second embodiment that thoughthe multi-divided light measuring sensor is designed to discriminatebetween the normal lighting condition and the back lighting condition, alight measuring sensor having a greater number of divided parts may beused to detect the distribution of brightness of the object (forexample, the proportion of the brighter portion to the whole brightarea), wherein the exposure control modes are selectively operateddepending on that detection result. For example, in a case where thelevel of brightness is extremely high (low) in part to the averagebrightness over the entire area of the picture, the preliminary exposureand the main exposure are carried out when taking one picture. Inanother case where the level distribution of brightness over the entirearea of the picture lies within a predetermined brightness level range,without having to make the preliminary exposure, only the main exposuremay be made when taking one picture. That is, in other words, when thecontrast of information within the picture is large, the preliminaryexposure is made, while when the contrast is small, the preliminaryexposure may be omitted.

As has been described above, according to the second embodiment of theinvention, the exposure can be controlled in optimum manner depending onthe distribution of brightness of the object, thereby it being madepossible to realize a high speed series of shots. Another advantage isthat a minimization of the size of the electronic camera body can beachieved.

Next, FIG. 6 through FIG. 9 show a third embodiment of the invention.And, FIG. 6 shows the arrangement of the circuit elements of the thirdembodiment, FIG. 7 shows the construction of a shutter mechanism, FIG. 8shows the running characteristic of the shutter when in AE mode, andFIG. 9 shows a flowchart.

In FIG. 6, light measuring means 28 comprises an AE sensor 17 and alight measuring circuit 17'. Computing means 29 comprises a comparisoncircuit 29' and a computing circuit 29". A shutter unit 30 comprises ahalf-open type shutter 30' and a shutter control circuit 30". An imagesensing unit 31 comprises an image sensor 1 and a signal processingcircuit 8. 32 is a switch. Judging means 33 comprises a comparisoncircuit 33' and a control circuit 33". A recording unit 34 comprises arecording circuit 34' and a recording deck 34".

The output of the AE sensor 17 of the light measuring means 28 is madeto be a light value by the light measuring circuit 17'. By putting thisinto the computing circuit 29" of the computing means 29, apredetermined exposure computation is performed. This computation datais put into the shutter control circuit 30" so that an opening andclosing operation is performed by the half-open type shutter 30'.Thereupon, optical image information enters the image sensing unit 31where an electrical image signal is formed. Also, from the informationoutput from the light measuring means 28, by comparing it with areference EV value V₂ in the comparison circuit 33', the control circuit33" judges whether or not the preliminary exposure is necessary fortaking a picture. Based on this judgment result, the switch 32 suppliesthe signal output from the image sensing unit 31 to either one of thecomparison circuit 29' of the computing means 29 and the recording unit34. In a case where it goes to the comparison circuit 29' of thecomputing means 29, there is an integration circuit INT on the way. Inthe comparison circuit 29' of the computing means 29, the signal iscompared with a reference exposure quantity V₁. A compensation is madeso that their difference becomes zero. This information is sent to theshutter unit 30 when the main exposure operation is performed. Afterthat, the image sensing unit 31 is read again and the signal isconducted through the switch 32 to the recording unit 34 and recorded.Incidentally, SC is a system controller for controlling the entirety ofthe circuit shown in FIG. 6, and TR is a trigger switch for recording astill picture.

Next, in FIG. 7, the shutter mechanism comprises an electric motor 101,a pinion gear 102, a speed reduction gear 103, a rack gear 104, rackguide pins 105 and 106 guiding the rack gear 104, a return spring 107for the rack gear 104, a clutch 108 pivotally mounted about a hole 104aof the rack gear 104 and urged by a clutch spring 109 so that its freeend engages a pin 110a of a control plate 110, an encoder 111 (pulsedisc) adhered on the control plate 110 and whose transparent portion111' is arranged to move across a photo-interrupter 113, a return spring112 for the control plate 110, diaphragm blades 114 and 115 guided bycommon guide pins 116 and 117 and having elongated slots 114a and 115arespectively into which respective pins 110b and 110c mounted on thecontrol plate 110 extend, and having openings 114b and 115b respectivelyforming a variable size of aperture, and an armature 118 of a magnetarranged upon supply of current to a coil 119 to rotate around a shaft120 in a counterclockwise direction until its free end 118a strikes aprotuberance 108b of the clutch 108 to release a pin 110a of the controlplate 110 from the engagement with the free end 108a of the clutch 108.

The operation is described below. At first the normal AE mode isdescribed. After the actuation of a release by the trigger switch TR,when the motor 101 rotates in the clockwise direction and the speedreduction gear 103 rotates in the counterclockwise direction, the rackgear 104 starts to slide to the right against the spring 107. The clutch108 mounted on the rack gear 104 also slides to the right. Therefore,the pin 110a of the control plate 110 is pushed by the free end 108a ofthe clutch 108 and the control plate 110 is rotated in thecounterclockwise direction against the spring 112, so that the diaphragmblade 114 is caused to slide to the left by the pin 110b and thediaphragm blade 115 is caused to slide to the right by the pin 110c.Thus, the diaphragm goes opening. At the same time, as the pulse disc111 on the control plate 110 rotates in the counterclockwise direction,the photo-interrupter 113 goes counting the transparent portion 111' ofthe pulse plate 111. When a predetermined pulse number is reached, thecoil 119 is supplied with current to attract the armature 118 upward.The free end 118a then strikes the protuberance 108b of the clutch 108so that the extension 108a is disengaged from the pin 110a. Therefore,the control plate 110 is rotated in the clockwise direction by thereturn spring 112, while its pins 110b and 110c returning the diaphragmblades 114 and 115 to thereby close the shutter. After that, the motor101 is rotated in the reverse direction, causing the rack gear 104 toslide to the left or to return to the initial position. Thus, a sequenceof operations ends.

The variation of the size of aperture opening in this sequence is shownin FIG. 8.

In FIG. 8, in the case of the AE mode, after the actuation of a camerarelease, the diaphragm is gradually opening. Along with this, the numberof pulses proportional to the aperture value as counted in connectionwith the diaphragm is increasing. When it has reached a predeterminedreference pulse number Pn, the magnet is energized. After a delay timeTm owing to the action of the magnet, the shutter is released from theconnection with the clutch and rapidly closes. This time lag results inproduction of an aperture opening error which amounts to ΔPm₁.

Next, in FIG. 9, as shown in the flowchart for the operation of thesystem controller SC of this embodiment, depending on whether the valueobtained by the light measurement is darker or brighter than a certainconstant value, control is made with selection of the following modes.

That is, the value obtained by the light measurement is converted intoan equivalent number of standard pulses. By comparing this number with areference pulse number, if the light value is determined to be darkerthan the certain value so that a long time is necessary for making theexposure, then skip over the step of making the preliminary exposure. Ifthe light value is brighter than the certain value, then make thepreliminary exposure.

In the following, explanation is made in greater detail. That is, whenthe trigger switch TR is actuated, the AE sensor 17 in the lightmeasuring means 28 detects the brightness of the object in a step S22.Its data is counted in the form of a number of standard pulses by thelight measuring circuit 17' in a step S23. Whether or not this countedvalue is larger than a counted value of the reference EV value V₁ isthen determined by the comparison circuit 33' in a step S24. By thiscomparison result, if the output of the AE sensor 17 is larger than thecounted value of the reference EV value V₁, as it implies that theobject is brighter than a predetermined level, the process then advancesto a step S25 where the motor 101 is turned on. Thereupon, as has beendescribed above, the shutter blades start to open. Thus, the preliminaryexposure is started (step S26). In accompaniment with this, the pulsedisc 111 rotates. Therefore, the photo-interrupter 113 counts the numberof passed gradients of the transparent portion (step S27), until itcomes to coincide with the aforesaid reference pulse number (step S28).When in coincidence, the magnet coil 119 is then supplied with a currentin a step S29. At the same time, the motor 101 is turned off.

By this, as has been described above, the control plate 110 rotatesunder the action of the bias spring 112, closing the shutter.

After that, in a step S31, the signal of the image sensor 1 is read andsupplied through the switch 32 to the integration circuit INT tointegrate the exposure quantity (step S32).

This integrated value is compared with the reference exposure quantityV₁ (step S33). Based on this comparison result (difference), thecomputing circuit 29" compensates the aforesaid reference pulse numberso that the aforesaid difference becomes zero in a step S34. In the nextstep S35, the motor 101 is turned on again, opening the shutter. Thus, amain exposure is started (step S36). Similarly to the step S27, thetransparent portion 111' of the pulse disc 111 is counted (step S37).Such a procedure is repeated until this counted value coincides with thecompensated reference pulse number (step S38). Upon coincidence, in astep S39, the magnet coil 119 is then supplied with a current and themotor 101 is turned off. The shutter is then closed in a step S40, thusterminating the shooting with the main exposure.

After that, as has been described above, the signal of the image sensor1 is read and supplied through the switch 32 to the recording unit 34and recorded as still picture information (step S41).

As has been described above, according to the third embodiment of theinvention, in a case where the opening and closing operation of theopening and closing members is determined to take a longer time than aconstant value based on the value output from the element for measuringthe quantity of light of the target to be shot, the preliminary openingand closing operation is not performed. Yet it becomes possible to carryout the exposure or opening and closing operation based on that valueoutput from the element for measuring the quantity of light of thetarget to be shot. In other words, the element for measuring thequantity of light of the target to be shot produces a value whichbecomes, for the first time, the reference value for the opening andclosing operation with the result of a non-exposure. Based on thisvalue, whether or not the non-exposure opening and closing operation hasto be made is judged so that even if there has been a change in therunning characteristic of the opening and closing members such as thediaphragm blades, the accuracy of control can be prevented from loweringdue to that change. Nevertheless, the camera does not becomeinconvenient to use in actual practice. Thus, the high accuracy ofexposure control can be preserved. Also, in a case where two consecutivecycles of opening and closing operation of the opening and closingmembers have been judged to be unnecessary, because the preliminaryopening and closing operation is not performed, or only one cyclesuffices, the number of times the shutter sound is produced is reduced.Moreover, there becomes no need to maintain the diaphragm stationary inthe open state for a long time.

Next, FIG. 10 shows the construction of a fourth embodiment of theinvention and FIG. 11 is a flowchart therefor. In this embodiment, anexposure operation is once performed based on the output of the lightmeasuring element. The video signal at this time is once stored in amemory. From this memory, the image information is non-destructivelyread out and whether it lies within a reference level range is tested.If so, then use the image information of the memory directly for therecording purpose. If not so, then use the image information stored inthe memory as the preliminary exposure data, based on which the error iscompensated for. After the exposure members have been controlled bytaking this compensation into account, another exposure operation iscarried out. This becomes the so-called main exposure.

The image information obtained by this main exposure is used inrecording.

Next, FIG. 10 and FIG. 11 are explained in detail, where the samereference numerals have been employed to denote the similar parts tothose shown in FIGS. 1 through 9. 35 is a provisional memory unit havinga D/A converter 35", a memory circuit 35' and an A/D converter 35'". 36is a switch. 32' is a switch.

Referring next to FIG. 11, an example of the manner in which the systemcontroller SC of the circuit of FIG. 10 operates is described.

The first steps S22-S31 are the same as in the flowchart shown in FIG. 9except that the step S24 is excluded. So, their explanation is omitted.The video signal of the CCD which has been transferred and read in thestep S31 is supplied to the switch 36 in a step S42. The output for thefirst time through the switch 36 is supplied through the A/D converter35'" to the memory circuit 35' and stored therein (step S42). Afterthat, in a step S43, this stored data on the memory circuit 35' isnon-destructively read out, then converted into an analog signal by theD/A converter 35", and then integrated by the integration circuit INT.Thus object luminance information is formed. Subsequently, thisluminance information is compared with the reference exposure quantityV₁ in the comparator circuit 29' in the step S33. Whether or not thedifference between it and the reference exposure quantity V₁ is largerthan a predetermined level is judged in a step S44. If the result ofthis judgment is that the difference is larger than the predeterminedlevel, then compensate the reference pulse number so that thisdifference becomes zero (step S45). After that, by the steps S35-S40,the main exposure operation is carried out based on the aforesaidcompensated reference pulse number.

Also, after that, the electrical signal output from the image sensor 1is transferred and read out in a step S47. This signal is suppliedthrough the switch 36 to the recording unit 34 and recorded on thefloppy disc in a step S48.

If, in the step S44, the difference between the luminance informationoutput from the memory circuit 35' and the reference exposure quantityis smaller than the aforesaid predetermined level, on the other hand,the video signal stored in the memory circuit 35' in the step S46 issupplied through the switch 32' to the recording unit 34 and recorded inthe step S48.

As has been described above, according to the invention, in the firstcycle of opening and closing operation with the result of anon-exposure, a value is detected which is once stored in the memorycircuit. This value is then integrated to obtain an exposure quantity.As it is compared with the reference exposure quantity, if theirdifference is larger than a certain value, the second cycle of openingand closing operation is then carried out by taking into account thecompensation of the value obtained in the non-exposure opening andclosing operation. If the difference is below the certain value, thevalue of the memory circuit is recorded as it is on the recording mediumsuch as a floppy disc, whereby the feedback exposure is not done as itis regarded as unnecessary. Thus, without causing anything wrong tohappen in actual practice, the exposure quantity can be controlled withhigh accuracy.

What is claimed is:
 1. An image sensing device comprising:(a) imagesensing means for converting an optical image into an electrical signal;(b) light measuring means, arranged separately from said image sensingmeans, for detecting light coming from an object to be photographed toform first light measurement data; (c) control means for controlling anexposure condition of said image sensing means, making a first exposureon said image sensing means in accordance with said first lightmeasurement data, and reading out an output of said image sensing meansformed by the first exposure to form second light measurement data; saidcontrol means also being operable to make a second exposure on saidimage sensing means in accordance with said second light measurementdata; and (d) recording means operating with selection of one of a firstmode in which the output of said image sensing means formed by the firstexposure is read out and recorded and a second mode in which the outputof said image sensing means formed by the second exposure is read outand recorded.
 2. A device according to claim 1, wherein said recordingmeans selects one of the first and second modes according to said firstlight measurement data.
 3. A device according to claim 1, wherein saidrecording means selects one of the first and second modes according tosaid second light measurement data.
 4. A device according to claim 1,further comprising flash illuminating means, and wherein said recordingmeans selects one of the first and second modes according to whether ornot said flash illuminating means is rendered operative.
 5. A deviceaccording to claim 1, wherein said recording means includes switch meansfor manually selecting one of the first and second modes.
 6. A deviceaccording to claim 5, wherein said switch means operates in associationwith a setting member for manually setting an exposure condition forsaid image sensing means.
 7. A device according to claim 6, wherein saidsetting member includes an exposure compensating member.
 8. A deviceaccording to claim 1, further comprising memory means for reading outand temporarily storing an output signal of said image sensing meansformed by the first exposure.
 9. A device according to claim 8, whereinsaid memory means includes a digital memory.
 10. A device according toclaim 8, wherein said recording means reads out and records a signalstored in the first mode in said memory means.
 11. A device according toclaim 10, wherein said control means forms said second light measurementdata on the basis of a signal read out from said memory meansnon-destructively.
 12. A device according to claim 1, wherein saidrecording means selects one of the first and second modes according to abrightness distribution of the object discriminated by said first lightmeasurement data.
 13. A device according to claim 1, wherein saidrecording means selects one of the first and second modes according tothe magnitude of a level of said first light measuring data.
 14. Adevice according to claim 12, wherein said recording means selects oneof the first and second modes according to whether the brightnessdistribution of the object discriminated by said first light measurementdata is a normal lighting condition or a back lighting condition.
 15. Adevice according to claim 12, wherein said recording means selects oneof the first and second modes according to a contrast of the brightnessdistribution of the object.
 16. An image sensing apparatus comprising:a)image sensing means for converting an optical image into an electricalsignal; b) first detecting means for detecting brightness of an objectand for forming a first detection signal; c) control means forcontrolling an exposure condition of said image sensing means andcausing said image sensing means to form a first electrical image signalbased on said first detection signal; d) second detecting means fordetecting brightness of said object based on said first electrical imagesignal and for forming a second detection signal, said control meanscausing said image sensing means to form a second electrical imagesignal based on said second detection signal; and e) recording means forselectively effecting a first mode for recording said first electricalimage signal and a second mode for recording said second electricalimage signal.
 17. An apparatus according to claim 16, wherein said firstdetecting means is arranged separately from said image sensing means.18. An apparatus according to claim 16, wherein said second detectingmeans includes integration means.
 19. An apparatus according to claim16, further comprising selection means for manually selecting said firstelectrical image signal and said second electrical image signal forrecording.
 20. An apparatus according to claim 16, wherein saidrecording means selects one of the first and second modes according tosaid first detection signal.
 21. An apparatus according to claim 16,wherein said recording means selects one of the first and second modesaccording to said second detection signal.
 22. An apparatus according toclaim 16, further comprising flash illuminating means, and wherein saidrecording means selects one of the first and second modes according towhether or not said flash illuminating means is rendered operative. 23.An apparatus according to claim 16, wherein said recording meansincludes switch means for manually selecting one of the first and secondmodes.
 24. An apparatus according to claim 23, wherein said switch meansoperates in association with a setting member for manually setting anexposure condition for said image sensing means.
 25. An apparatusaccording to claim 24, wherein said setting member includes an exposurecompensating member.
 26. An apparatus according to claim 16, furthercomprising memory means for reading out and temporarily storing thefirst electrical image signal.
 27. An apparatus according to claim 26,wherein said memory means includes a digital memory.
 28. An apparatusaccording to claim 26, wherein said recording means reads out andrecords a signal stored in the first mode in said memory means.
 29. Anapparatus according to claim 28, wherein said second detecting meansforms said second detection signal on the basis of a signal read outfrom said memory means non-destructively.
 30. An apparatus according toclaim 16, wherein said recording means selects one of the first andsecond modes according to a brightness distribution of the objectdiscriminated by said first detection signal.
 31. An apparatus accordingto claim 16, wherein said recording means selects one of the first andsecond modes according to the magnitude of a level of said firstdetection signal.
 32. An apparatus according to claim 16, wherein saidrecording means selects one of the first and second modes according towhether the brightness distribution of the object discriminated by saidfirst light measurement data is a normal lighting condition or a backlighting condition.
 33. An apparatus according to claim 30, wherein saidrecording means selects one of the first and second modes according to acontrast of the brightness distribution of the object.